The invention relates to a fuel injection valve for internal combustion engines Fuel injection valves of this kind have been disclosed, for example, by DE 195 47 423 A1 and DE 196 34 133 A1.
In fuel injection valves of this kind, a piston-shaped valve member is guided so that the valve member can move axially in a bore of a valve body, On its end oriented toward the combustion chamber, the valve member has a conical valve sealing surface with which it cooperates with a conical valve seat surface on the valve body, the valve seat surface being formed at the inward protruding end of the closed valve bore. The valve sealing surface on the valve member is divided into several, preferably two, regions with different cone angles, and a transition region is provided between the two valve sealing surface regions, which is delimited by a downstream and an upstream valve sealing edge.
Due to the high valve closing forces that occur particularly in these fuel injection valves of the xe2x80x9chole nozzle typexe2x80x9d, an asymmetrical jet pattern occurs, particularly with very small strokes of the valve member or during the prestroke when there are two spring retainers, and this asymmetrical jet, pattern leads to an increase in emissions of the internal combustion engine. The valve member adapts to the nozzle body elastically as a result of the valve closing force. In this case, the hydraulically effective seat diameter thus produced is indefinitely disposed in the transition range, as schematically depicted in FIG. 1. The inverse seat angle differential produces a pressure distribution on the axially offset valve member, which presses the valve member back into the central, axial position. By contrast, in a fuel injection valve without an inverse seat angle differential, a pressure distribution would be produced which would move the valve member even further away from the central, axial position.
An object of the invention is to modify a fuel injection valve of this generic type in such a way that the axial alignment of the valve member permits the production of a symmetrical jet pattern. The invention also permits the production of a definite hydraulically effective seat diameter, a high degree of damping of the valve member, and the least possible risk of cavitation.
In a fuel injection valve of the type described at the beginning, this object is attained according to the invention and particularly with increasing wear on the fuel injection valve. The fuel invention valve has the advantage that by means of the radial, undercut-shaped recess embodied in the valve member upstream of the transition region and by means of the inverse seat angle differential, the hydraulically effective seat diameter can xe2x80x9ctravelxe2x80x9d maximally to the upstream valve sealing edge. This produces a precisely defined hydraulically effective seat diameter at the upstream valve sealing edge.
The distance between the upstream and downstream valve sealing edges of the transition region is selected so that the upstream valve sealing edge of the transition region constitutes the hydraulically effective seat diameter. The distance can be determined by means of experimental measurements arid/or calculations.